This invention relates in general to movable bolsters/carriages for metal working presses, and more particularly to a retractable wheel assembly for movable bolsters/carriages which provides the bolster/carriage with greater flexibility in directional movement.
A metal working press is a heavy type of machine designed to receive, press and shape metal to the contours of a die. The die used to work the metal generally have weights of 25-150 tons, and for certain applications can be even heavier. A bolster is a plate attached to the top of a press bed or carried upon a movable carriage. A carriage is an open box of welded steel construction carried upon carriage wheels, upon which a bolster and/or die is attached. The term bolster/carriage is used in the present application to mean a bolster and/or carriage in combination or separately. The bolster/carriage is generally powered by a reversible pneumatic motor or the like, coupled through reduction gears to a pair of carriage wheels. The bolster/carriage is utilized to carry the die between a loading area and a press structure on a system of tracks. The tracks are generally constructed of heavy, machined I-beams capped with replaceable rail strips. When the bolster/carriage is positioned in a die area, rail sections beneath the wheels retract, setting the bolster/carriage firmly on the press bed. The bolster/carriage is then securely clamped in place with automatic clamps to provide a firm, stable platform for the bottom half of the die. The upper half of the die is affixed to the press for movement against the bottom half of the die.
Earlier bolster/carriages were capable of carrying dies along a linear track layout from a loading zone to the press site. However, present day production demands and space requirements have encouraged the use of bolsters/carriages and track layouts which are more flexible. Many track layouts now mandate use of bolsters/carriages capable of travel upon orthogonally aligned intersecting tracks.
In order to accommodate orthogonal travel, present bolster/carriages are equipped with one set of four wheels engageable with one set of tracks, and a second set of four wheels, aligned at 90.degree. angles with respect to the first set of wheels, engageable with a second set of orthogonally aligned tracks. One set of orthogonal wheels is actuated hydraulically through a system of hydraulic cylinders and levers to engage its associated tracks, while the other set is raised to a disengaged position relative to its associated track.
In order to change from a simple in line track layout to the more orthogonal complex track layout just described, not only does the track system need to be changed but the entire bolster/carriage system has to be replaced at considerable expense. Further, the necessity of the bolster/carriages having two sets of four wheels with only one set being used at any one time is deemed to be unnecessary duplication and add to the cost of manufacture.